Field of the Invention
The present invention relates to an expandable composite resin bead, which comprising a blowing agent and a composite resin containing a polyethylene resin and a polystyrene resin.
Description of the Background Art
A foamed resin molded article formed from expanded beads obtained through in-mold molding and mutual fusion-bonding of the expanded beads is widely used in applications such as for wrapping materials, building materials, impact absorbing materials, and the like, by utilizing excellent properties of the foamed resin molded article including buffering property, lightweightness, thermal insulation property, and the like. As the foamed resin molded article, those whose base resin materials include a polyolefin resin such as polypropylene and polyethylene or a polystyrene resin such as polystyrene are used.
When compared to a foamed polystyrene resin molded article formed from the expanded beads, a foamed polyolefin resin molded article formed from the expanded beads has excellent impact resistance, toughness, and post-compression restorability, and is therefore used as packaging materials and wrapping materials for precision components and heavy weight products etc. Furthermore, the foamed polyolefin resin molded article also has excellent heat resistance and oil resistance, and is therefore also used as automobile components such as impact absorbers, bumpers, and floor spacers. In such manner, the foamed polyolefin resin molded article is widely used in various applications.
However, although the foamed polyolefin resin molded article has excellent characteristics as described above, the foamed polyolefin resin molded article also has shortcomings including having low rigidity and requiring equipment such as special metal molds since the steam temperature upon in-mold molding is high, when compared to the foamed polystyrene resin molded article.
On the other hand, when compared to the foamed polyolefin resin molded article, the foamed polystyrene resin molded article is generally moderate in price, has low molding vapor pressure upon in-mold molding, and has fine processability, and is therefore widely used in the market. Furthermore, the foamed polystyrene resin molded article has excellent rigidity, and enables a high foam expansion ratio depending on the application. Thus, when compared to the foamed polyolefin resin molded article, the foamed polystyrene resin molded article is also advantageous in terms of lightweightness.
However, when compared to the foamed polyolefin resin molded article, the foamed polystyrene resin molded article also has shortcomings such as having inferior toughness and post-compression restorability.
In order to resolve shortcomings of both molded articles described above, for example, technologies described in the following have been developed.
More specifically, methods have been developed for obtaining modified polyethylene resin beads by impregnating polyethylene resin nuclear beads with a vinyl aromatic monomer, polymerizing the vinyl aromatic monomer, and crosslinking the polyethylene resin (cf. JP45-32623B2 and JP1-284536A).
In addition, a method has been developed for producing expandable polyethylene resin beads by preparing polyethylene resin nuclear beads from an acrylonitrile-styrene copolymer and a polyethylene polymer, impregnating the nuclear beads with a styrene monomer, polymerizing the styrene monomer, and impregnating the resin beads with a blowing agent (cf. JP2007-321021A).